I'm not able to reproduce this issue on my device. After dragging the Family Proclamation to the left, the drag and drop area lights up red, as expected, and, as I let go, as the 'book' to the very bottom of the collection list. Have you tried restarting the app?

Learn more about Gospel Library for Windows 10 Beta at the link below:https://tech.lds.org/wiki/Gospel_Library_for_Windows_10

I figured out my problem. I wasn't at the proclamation level. When the top level said "family" and had an image of the proclamation I assumed that was the family proclamation. I didn't realize it was the overall topic.